


Double Dog Dare You

by Nillas NSFW Corner (Agraulis_vanillae)



Category: Undertale (Video Game)
Genre: Alternate Universe - Swapfell, Alternate Universe - Underfell, Alternate Universe - Underswap, Anal Fingering, Ecto-Penis (Undertale), Food, Food Poisoning?, M/M, Oral Sex, Sans - Freeform, Smut, They just live in the same house for convenience sakes, Underfell Sans, kustard - Freeform
Language: English
Status: Completed
Published: 2017-02-04
Updated: 2017-02-04
Packaged: 2018-09-21 21:24:12
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,567
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/9567179
Author URL: https://archiveofourown.org/users/Agraulis_vanillae/pseuds/Nillas%20NSFW%20Corner
Summary: Sans takes a dare he's not sure he should've taken. It involves ancient takeout.





	

**Author's Note:**

  * For [YaoiAddiction](https://archiveofourown.org/users/YaoiAddiction/gifts).



> I don't think I got too graphic with it, but there may be a gross-out component. Good luck!

“OKAY SERIOUSLY, WHOSE IS THIS?!! IT'S BEEN HERE FOR OVER A MONTH NOW, AND I'M SERIOUSLY NOT GOING TO BE THE ONE TO HAVE TO TOUCH IT.” Blackberry shouted from the kitchen. “SLIM!!!”

 

It wasn't long before everyone was summoned into the kitchen, as Slim was ordered. The object in question was a bag of leftover Grillby's that had been left in the fridge much too long. The bottom of the paper take out bag was soaked with a questionable substance that could have been grease but for the fine white growth of fuzzy mold that had taken root there.

 

“P-PAPY, IT'S L-LEERING AT ME!!” Blueberry squeaked tremulously, keeping a wide distance from the bag. He looked simultaneously repulsed and terrified as to what the contents of the bag might be.

 

Swap slowly approached the bag, and Blackberry hissed, “DO NOT. OPEN THAT. WHILE I'M HERE.”

 

He raised his hands in surrender, “my bad. it looks like a grillby's bag, so that leaves slim and i out. We head to muffet's place when we go out to eat.”

 

Papyrus nodded thoughtfully, “OH RIGHT, YOU DO, DON'T YOU? WHICH MEANS...”

 

“WHICH MEANS THAT EITHER MY BROTHER OR SANS ARE RESPONSIBLE FOR THAT ATROCITY IN OUR FRIDGE!” Fell growled menacingly, as he laid a hand on Red's shoulder, digging the sharpened tips of his phalanges into the clavicle and anchoring his sweating brother there. “WAS IT YOU, DEAREST BROTHER?”

 

“uh, I don't remember boss!” Red sputtered, the truth was out before the thought to lie occurred to him, the piercing force of Fell's grip threatening to draw marrow.

 

“tibia honest bro, i don't actually remember if it was me either.” Sans confessed.

 

“THEN EITHER OF YOU HAVE TO GET RID OF IT! IT LOOKS LIKE IT'S ABOUT TO GROW HYPHAE AND SLIT OUR THROATS AS WE SLEEP!” Blackberry ordered, his face screwed up in distaste.

 

“or tentacle fuck us...” Slim muttered, eyes casting over Blueberry appreciatively and earning a dark look from Swap for his trouble.

 

Next thing Sans and Red knew, everyone was evacuating the kitchen, leaving them as the designated sacrifices to the moldy takeout bag.

 

“you sure you don't remember leaving it in here?” Red asked Sans, and he raised two fingers in an oath.

 

“scout's honor.” he responded, shuffling closer to edge the bag open and peer inside.

 

Red grumbled, “none of us were scouts, including you.”

 

“lies, i was a sailor scout one halloween for papyrus.” Sans argued with an amused smile, and Red nearly bent over guffawing for a second at the mental picture. “as the cool guy that he is, he was apparently helping out alphys for a costume party contest.”

 

“we... really are suckers for our brothers, aren't we?” Red wheezed, regaining himself and seeing Sans staring dubiously into the bag. “what's in it?”

 

“both fries and the burg. it looks... surprisingly intact.” he observed. “i don't think the mold's touched the food in here at all.”

 

“so, it's still safe to eat?” Red asked, more curious than grossed out at this point. “heh, maybe you should eat it and just get it over with.”

 

Sans tilted his skull away, fixed grin still in place as he closed his eyes briefly. “oh yeah? eat me.”

 

It was meant as a sarcastic response, and Sans was already rolling up the top of the bag ready to toss it in the garbage when Red shrugged, “sure, why not.”

 

He paused mid-turn, “why not, what?”

 

“eat ya.” Red smirked, leaning across the table. It wobbled forward for a second, and he stood up straight again before it could dump him to the ground. Redirecting his attention to Sans who was still waiting for an explanation, he closed both eyes for a moment only to open them with an even toothier smile, “i dare ya to eat what's in that bag, and i'll blow ya for it.”

 

Sans deadpanned, “no way.”

 

“what?!! are ya a scaredy cat?” Red huffed, annoyed at the easy rejection. “fine! i double dog dare ya!!!”

 

A pause. Daring was one thing, but double-dog dares was a matter of honor. Sans may be lazy, but he certainly wasn't a scaredy cat. “all right, but you're going to take over my work stations if this becomes the claws for puking later.”

 

Red watched, grinning gleefully in anticipation as Sans reluctantly pulled the soggy fries and ages old burger out of the bag. A sadistic thought occurred to him as Sans's eyesockets went hollow in disdain. “i think that'll be purrfectly fine without ketchup, don't you?”

 

“that's ruff buddy. why do we even hang out?” To Sans's credit, he didn't gag as he unwrapped the burg and took his first bite, but his bones certainly took an unnaturally chalky appearance as he blanched. He didn't chew as much as he pushed it around in his jaw experimentally, and then tossed his head back to swallow it whole.

 

“how is it?”

 

“the lettuce is slimy.” Sans grunted, and then took another heroic bite. Red knelt on his knees and tugged down Sans's athletic shorts. Nothing had coalesced yet, but that wouldn't be a problem for long, even if Sans nearly choked trying to swallow the next chunk. “w-whoa whoa whoa! i thought the offer was for after i finished eating?”

 

Red grabbed his hips, and pushed him into the kitchen chair, before letting his tongue manifest in his mouth. “i didn't say when.”

 

Red let excess drool gather in his mouth before laving a long lingering lick across Sans's pubic symphysis. He reached beyond Sans's hip to fondle the tip of his tailbone before biting hard into his femur. Sure enough, magic began rushing down, and Red eyed the blue rush into the cradle of Sans's pelvis hungrily. Regardless, Sans still hadn't continued eating since the last bite and Red reminded him with another piercing bite to his other femur,

 

“get eating or you're going to have a bad time.”

 

Sans didn't even look at the burger before he tossed the rest of it in his mouth, profoundly grateful that he couldn't taste it without magic, though such a large chunk did have to be chewed. The bun didn't tear as much as it broke into leathery chewy pieces, and there was no denying the sneaking suspicion that lettuce shouldn't squirt like that under pressure. The whole thing was a chewy, solid mass and he could feel it mixing in with his magic uneasily.

 

Fortunately, it was enough to satisfy Red, who'd began mouthing at the magic cradled in his pelvis. The mini-shock waves of heat was just enough to get a member formed, and next thing he knew, Red's tongue was flattened out against the bottom of his shaft, the tip of his tongue dragging up against one of the veins of magic. Red groaned with satisfaction as Sans moaned, eyelights getting hazy.

 

“the fries too.” he prompted huskily, scraping the tip of his phalanges against his tailbone.

 

“that's the least sexy thing you could possibly say in that tone, right now.” Sans's moans turned into a drawn out groan, and he started shaking the box of flaccid fries into his mouth.

 

Then Red drew Sans's head into his mouth, and began to suck hard, the tip of his tongue probing into the slit of his member. Sans choked for a moment, and then managed to control the reflexes of his magic to allow the rest of the starchy food to pass. Red stopped sucking with a mute popping sound, to wink cheekily, “ain't it ironic i'm blowing you and you're the one that has to restrain a gag reflex?”

 

Sans merely flipped him off before placing a palm over his skull and pushing him back onto his dick impatiently. Red let him, showing off by deep-throating him all at once. He stopped fingering Sans's tailbone to hold his hips down and swallow around his dick.

 

“hnn...” Sans whined lowly, reflexes attempting to buck deeper into the sudden tightness of his throat. He nearly missed his mouth shaking out the last of the french fries and attempted to simply inhale them all at once, when Red upped the game and pushed a finger into the magic underneath the tailbone. Sans choked, “hurk!! ugh, ulk!”

 

Red continued swallowing around him for a few seconds, drool pooling and dripping out the corners of his jaw. He began thrusting the digit in to encourage thrusting forward as he bobbed his head. His tongue wrapped around the bottom of Sans's throbbing shaft and then head of his cock nudging the back of his throat where it was gripped by Red's skillfully timed gulping. Sans felt his end hitting quick, and grunted out in warning, “i'm about to-”

 

Red pulled off, tongue pressed against the head and stroking him rapidly, squeezing firmly just as Sans's orgasm hit. Streams of cum hit Red's entered his mouth, but also hit him full in the cheek. Face dripping, Red stood up to lean over Sans, who was still panting with his eyes closed from both the exertion and choking.

 

“hey buddy, hold up your end of the deal.” Red growled lowly. Sans opened his eyes only for his sockets to widen at the sight before him. His twin's crimson eyes bore into him searingly, cum traveling slowly down his cheekbone, his mouth glimmering with drool and semen. “you missed some mayo.”

 

**Author's Note:**

> This is a dare Yaoi gave me literal months ago! I can't believe it took me this long. The dare was basically food porn involving hamburgers and french fries, so I took it an extra step and made it a dare-ception. This may not have too much editing involved, so I apologize for any mistakes that has gone unnoticed.


End file.
